Emulsion developers for photoconductography



P 1968 1. B. VlLLE 3,402,111

EMULSION DEVELOPERS FOR PHOTOCONDUCTOGRAPHY Filed Jan. 22, 1965 STEP B w Q a IVAN B VILLE p INVENTOR.

TTOR/VE KS United States Patent 3,402,111 EMULSION DEVELOPERS FOR PHOTOCONDUCTOGRAPHY Ivan B. Ville, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Jan. 22, 1965, Ser. No. 427,289 8 Claims. (Cl. 20418) ABSTRACT OF THE DISCLOSURE An electrophoretic photoconductographic process in which an emulsion comprising an oily discontinuous phase and an aqueous continuous phase is used for developing an image exposed on a photoconductive surface. The oil phase is used as a carrier for a suitable dye or pigment, as a leach for removing color already present in the photoconductive material or as a carrier cfor a leaching agent. The image can be made to appear in any desired color and with the use of suitable pigments, the image densities can be higher than those obtained with the use of conventional silver salt developers.

This invention relates to photoconductography. More particularly, it relates to photoconductographic systems in which stabilized oil-in-water emulsions are used to develop the image.

Electrolytic photoconductography is well known, being described, for example, in Von Bronk British Patent No. 188,030, Goldmann British Patent No. 464,112, and Johnson et al. US. Patent No. 3,010,883. In electrolytic photoconductography, a reproduction of a desired image is formed on the surface of a photoconductive layer such as zinc oxide in resin, by projecting the desired image onto the surface and thereafter developing the image, typically by electrolytically depositing on the surface a metal such as silver in accordance with the projected image.

The present invention differs from the photoconductographic methods heretofore known in that an emulsion comprising an oily discontinuous phase and an aqueous continuous phase is used for developing the desired image. The invention can be practiced in several variations. In one of these, the oil phase carries a dye dissolved therein which [forms a visible image on the photoconductive surface. In another variation, the oil carries a solid pigment to develop the image, while, in still another variation, the oily phase is used to leach an existing color out of the photoconductive surface in an imagewise manner. The invention can further be practiced in a manner to produce either positive or negative images relative to the original material, as described.

The emulsion developers used in the invention are essentially oil-in-water type emulsions in which the oil phase is a solvent or semi-solvent for the binder or a material, such as a resinous substance, capable of adhering to the surface in which the photoconductive material is maintained. The emulsions are stabilized with suitable surface active agents to permit deposition of the oil at the surface of the photoconductive material. The oil phase is used as a carrier for a suitable dye or pigment contained therein, as a leach for removing color already present in the photoconductive surface, or as a carrier for a leaching agent.

The system of the invention has a number of advantages compared to the conventional electrolytic developing methods heretofore known. The image can be made to appear in any desired color, limited only by the availability of suitable oil-soluble dyes, which can be used singly or in combination as desired. The stability of the images produced in accordance with the invention is obviously dependent on the fade resistance of the dyes employed. Because of the fact that the oils are absorbed into the photoconductive surface, however, the resistance of the image to mechanical damage is excellent. The use of emulsions as developing agents in accordance with the invention has the further advantage of flexibility in operation since the basic technique of the invention can be used to produce positive-to-positive or negative-to-positiv reproductions in a wide variety of colors as desired. In addition, by use of suitable pigments, image densities 'higher than those obtainable with conventional silver salt developers can readily be obtained.

The invention can be carried out in a manner to achieve negative-to-positive or positive-to-positive reproduction as desired.

Negative-to-positive reproduction is accomplished by incorporating one or more oil-soluble dyes or solid pigments in the oil phase of the developer prior to emulsification. Imagewise illumination of the photoconductive surface followed by electrophoretic development with the emulsion results in deposition of the dyeor pigmentbearing solvent onto the exposed areas of the photoconductive surface, giving a negative reproduction of the original image. The reproduction thus formed is resistant to mechanical damage-because of the tendency of the solvent to diffuse into the photoconductive layer rather than to deposit on its surface.

The method used to obtain a positive reproduction involves first illuminating the desired image onto a photoconductive surface followed by development of the surface with an oily emulsion developer in which the oil contains no dye or pigment. This treatment causes deposition on the photoconductive surface of an oily invisible or nearly invisible layer in an imagewise manner which acts as a stencil for subsequent visible development. The areas which had been exposed to light are rendered electrically insensitive as a result of this treatment whereas the areas on which no light had fallen retain their photoconductive properties. The photoconductive surface is then given an overall exposure to light and developed vw'th a developer which deposits image-forming material (e.g., a dye or a'solid pigment in accordance with the invention, or a metal following conventional practice) in the areas which remain sensitive, thus producing a positive reproduction of the original image.

The invention will be better understood [from the following detailed description thereof, taken in conjunction with the accompanying drawings, in which like numerals are used to represent identical objects in the several views and in which:

FIGURE 1 is a schematic representative of a typical method employed in producing negative-to-positive reproductions in accordance with the invention; and

FIGURE 2 is a schematic representation of the process by which positive-to-positive reproductions are made.

Referring to FIGUREI, in a typical embodiment of the method of the invention used for negative-to-positive reproduction, a transparency 10, typically containing light or clear areas 11 and dark areas 12 constituting a negative representation of the desired image, is projected (step A) by means of lamp 13, reflector 14, and lens 16 onto a photoconductive surface (e.g., Zno in resin) 17 supported on a conductive sublayer 18, typically aluminum foil. After being exposed for the necessary time, the photoconductive surface 17 is immersed (step B) in a developing system comprising an emulsion 21 of an oil (carrying a soluble dye or finely divided pigment) in water held in a suitable container 22. The conductive sublayer 18 supporting the photoconductive surface 17 is connected to the negative terminal of battery 23 (schematically representing a source of potential) through variable resistor 24 used to control the flow of current between the surface 17 and anode 26, made of any suitable conductor such as copper, connected to the positive terminal of battery 23. The flow of current between anode 26 and surface 17 (cathode) causes the accumulation on the surface 17 of dye or pigment in dark zones 27 representing those portions of the surface which were exposed to light in step A. It will be seen that these darkened areas bear negative relationship to the original image carried by transparency 10.

FIGURE 2 depicts schematically the steps in a process by which positive-to-positive reproduction is made. After exposure of the photoconductive plate as described above (step A), the photoconductive surface 3 1 with its conductive sublayer 32 is developed (step B) in a bath 33 comprising an emulsion in water of an oil containing no dye or pigment, which collects on the photoconductive surface 31 in zones 34 corresponding to the areas in which light passing through the transparency 10 fell on the photoconductive surface. The oil in zones 34, which is invisible or nearly so, desensitizes the areas of the photoconductive surface 31 with which it is in contact. In step C, the photoconductive surface is exposed to overall illumination from lamp 13, the oil zones 34 now acting as a stencil to control the areas of the surface 31 which become conductive as a result of the exposure to light. In step D, the photoconductive layer 31 is developed as described previously in conjunction with FIGURE 1. The developing bath 36 can be an oil emulsion in which the oil carries a dye or solid pigment in accordance with the invention or, alternatively, may be a conventional electrolytic solution of a metal salt. In either case, darkened image zones 37 are formed which correspond to the dark areas of the original transparency, thereby producing a positive reproduction.

As an alternative to the above-described method of practicing the invention in which a visible dye or pigment is carried by the oily emulsion and deposited on the exposed photoconductive surface to reproduce the desired image, the invention can also be carried out in such a manner that the oily emulsion removes color from a suitably prepared photoconductive surface. Positive-topositive reproduction in this manner can be accomplished in accordance with the invention by incorporating a leachable dye into the photoconductive material-in-resin-mixture before the material is coated on the image-receiving surface. The amount of dye used should be sufficient to produce a fairly dark coating capable of giving sufficient contrast in the final print. When this surface is exposed to a desired image and developed with an emulsion of a leaching agent, the leaching agent is deposited in the image areas of the print. The surface active agent leaches out the dye in those areas leaving a positive representation of the original image.

This invention is illustrated by the following examples.

EXAMPLE 1 Negative-to-positive reproduction was carried out in the following manner using an oil-soluble dye.

500 cc. of distilled water was placed in a quart Waring Blendor and drops of Catanac SP (a cationic surface active agent comprising stearamidoisopropyldimethyl-B- hydroxyethylammonium phosphate) was added to it and mixed in. A solution of 5 cc. Freon 112 (l,1,2,2-tetrachloro-1,2-difluoroethane), 0.1 g. of a disazo type solvent black (class 3, color index No. 26150), and 5 drops Duomeen S (an N-alkyl-trimethylenediamine derivative of soybean oil, was added rapidly to the water while the blender was running at medium speed, forming an oil-inwater emulsion.

The resulting emulsion was diluted 1/1 with distilled water and placed in the bath machine. A ZnO-in-resin photoconductive coating was placed in contact with a transparency and given a 500 ft.-c. sec. exposure from a 500-watt slide projector. The exposed coating was developed in a photoconductographic developing machine at a transport speed of approximately 0.3 in./sec. and a potential of 60 V. DO. applied between the anode and the exposed coating. The emulsion was agitated between prints by a small 3-bladed propeller turned by an air motor. The agitation was turned ofi just prior to the making of each print.

This resulted in the deposition of the Freon/solvent black phase of the emulsion in the exposed areas of the coating, thus producing a negative-to-positive reproduction of the original transparency.

EXAMPLE 2 Positive-to-positive reproduction is illustrated in this example.

891 cc. of distilled water was put in a quart Waring Blendor. Five drops of Catanac SP was added and mixed in. The Waring Blendor was turned on at medium speed an 9 cc. .p-chlorotoluene was added rapidly to form an emulsion of p-chlorotoluene in water.

The resulting emulsion was diluted 1/1 with distilled water and was placed in a bath-type developing machine. A piece of photoconductographic paper was placed in contact with a transparency and given a 400 ft.-c. sec. exposure from a 500-watt slide projector. The paper was placed on the drum of the developing machine and run in contact with the surface of the emulsion at a transport speed of approximately 0.3 in./sec. with an applied potential of volts between the anode and the exposed sheet. The width of the area of contact between developer and paper was about 1 inch.

The paper was then removed from the drum, blotted, and dried in air. It was then given an overall 400 ft.-c. sec. exposure and developed with 1 stroke (about 2 in./sec.) of a l-inch viscose sponge wet with a silver complexed electrolytic developer (silver nitrate thiourea complex) with a potential of 40 V. DC. between the anode and the exposed sheet. In all cases the aluminum foil backing of the photoconductive ZnO-in-binder coating was held negative with respect to the developing medium.

This treatment resulted in the deposition of silver in the areas corresponding to the non-image areas of the first exposure, thus producing a positive-to-positive reproduction of the original transparency.

EXAMPLE 3 An emulsion developer was made by adding 5 g. of a mixture of the oil phase comprising 16 cc. toluene, 4 cc. Freon 112, 1.8 cc. 20% Alkaterge T (substituted oxazoline surface active agent, and 3 g. solvent black dye to a water phase comprising 4.5 cc. of 35% Catanac SP and 500 cc. of distilled water. The mixture was dispersed in a Waring Blendor for 1 min., and finally dispersed in a hand homogenizer at medium spring tension.

A strip of zinc oxide-resin photoconductographic paper was placed in contact with a negative transparency and given a 550 ft.-c. sec. exposure from a 500-watt slide projector through a 0.3 density increment step wedge. The exposed coating was dipped into an electrophoretic cell containing the above-described emulsion developer, and a potential of 80 volts D.C. was applied in which the photoconductive coating was held negative with respect to the developing solution for 1 sec. A brass electrode (anode) in the cell was about 0.06 in. from the paper being processed; the aluminum foil laminate of the paper comprised the cathode.

The oil phase was deposited in the exposed areas of the photoconductographic paper leaving a bluish black positive image with a maximum density of 1.35 (unlacquered) and 1.91 (with a water-soluble lacquer overcoat comprising a copolymer of methyl methacrylate and methacrylic acid).

EXAMPLE 4 The use of a pigment in the oil phase is illustrated in this example.

A dispersion was made of 330 g. Freon 112, 400 drops Duomeen S, 20 g. an inorganic pigment black, and 2 g. Pliolite S-7 (copolymer of butadiene and styrene) and mixed for 5 min. in a Waring Blendor.

Three cc. of the above dispersion was added to 500 cc. of distilled Water containing 5 drops of Catanac SP, all in a Waring Blendor. The resulting emulsion was put in a sparatory funnel and subsequently drawn off to remove the froth which formed at the top.

The emulsion was then placed in a bath-type developing machine. A ZnO-in-resin photoconductive coating was placed in contact with a transparency and given a 500 ft.-c. sec. exposure from a 500-watt slide projector. The paper was placed on the drum of the developing machine and run in contact with the developer at a transport speed of about 0.3 in./sec. with an applied potential of 100 volts between the anode and the exposed paper. The width of the area of contact between developer and paper was approximately 1 inch.

The paper was then removed from the drum, rinsed, and dried in air. This treatment resulted in a negative, carbon black reproduction of the original transparency.

EXAMPLE 5 The use of an oil-in-water emulsion to leach dye out of a photoconductive surface is illustrated in this example.

Ten cc. of Glaurin (diethylene glycol monolaurate) were added, with stirring, to 200 cc. of distilled water containing 2 cc. of Catanac SP. The resulting crude emulsion was passed through a hand-powered homogenizer and placed in a 250 cc. beaker.

A mix of ZnO in binder with the addition of sufficient solvent black to produce fairly dark background color was made and coated (0.003 in. thick) on aluminum foilpaper laminate, dried, and dark adapted.

A section of the resulting coating was exposed to 135 ft.-c. of illumination for 7 /2 sec. through a positive transparency. The exposed coating was clipped to the negative lead of a DC. power supply and inserted into a beaker containing the emulsion and a copper anode. A twenty volt potential was applied between the anode and exposed paper for 30 sec. The coating was then removed, rinsed, blotted, and hung up to dry.

Deposition of the Glaurin in the print areas corresponding to the non-image areas of the transparency resulted in the leaching out of the solvent black in these areas, thereby producing a positive representation of the original transparency.

The use of emulsions as developing agents for photoconductographic systems has been described in conjunction with the use of zinc oxide as a typical photoconductive material. As those skilled in the art appreciate, in systems employing zinc oxide, the zinc oxide is made the cathode during electrolytic development. For use with zinc oxide photoconductive surfaces, therefore, a cationic surface active agent is used in the invention to stabilize the oil-in-water emulsion in order to insure deposition of the oil at the cathode under the influence of the applied potential, which, in accordance with the usual practice, involves making the zinc oxide layer negative. It should be understood, however, that, in the event a different photoconductive material is used which is made the anode in the developing system, the emulsions of the invention would be stabilized with anionic surface active agents in a similar manner. In any event, cationic and anionic surface active agents suitable for use in the invention will be readily apparent to those skilled in the art. Other surface active agents which can be used include, for example:

Water phase Emcol--N(lauroyl colamino formyl methyl)pyridinium chloride Atlas--N-soya-N-ethyl morpholinium ethosulfate AmmonyxStearyl dimethyl benzyl ammonium chloride Penetronyx--Alkyl dimethyl hydroxyethyl ammonium bromide Oil phase KatapolPolyoxyethylated a'lkylamine n-Dodecylamine Intracol-OLong chain fatty acid amide No discussion of relative proportions of dyes, pigments, concentrations of surface active agents, etc., has been given because these vary widely depending on the specific identity of each such ingredient, as will be apparent to those skilled in the art, and because these specific quantitles are not the essence of the invention. The selection of suitable dyes, pigments, surface active agents, and the like, can readily be made by one skilled in the art to achieve satisfactory results.

In addition to the particular oils which have been used by way of example in the specific examples given above, a wide variety of other materials can be used. The most important characteristic of the oil phase in the emulsion is that it should have the ability to penetrate or be absorbed into the binder of the photoconductive layer or adhere to the surface thereof. Similarly, although water is the preferred material for the continuous phase of the emulsions used in the invention, other materials can also be used. Such materials should be relatively non-volatile, immiscible with the oil phase, and should have no harmful effect on the sensitivity of the photoconductive layer.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. In a photoconductographic process in which an image pattern of variations in electrical conductivities is produced in a layer comprising a photoconductive material, the steps of exposing said photoconductive material to a desired image pattern and establishing a potential difference between said exposed photoconductive material as a first electrode and a second electrode in the presence of a stabilized oil-in-water emulsion in contact with said electrodes.

2. The process of claim 1 in which said photoconductive material is the cathode and said second electrode is the anode and in which said oil-in-water emulsion is cationically stabilized.

3. The process of claim 1 in which said photoconductive material is the anode and said second electrode is the cathode and in which said oil-in-water emulsion is anionically stabilized.

4. The process of claim 2 in which the oil phase of said oil-in-water emulsion contains dissolved therein a visible dye.

5. The process of claim 2 in which said oil phase has incorporated therein a finely divided pigment.

6. The process of claim 5 in which said pigment is carbon black.

7. The process of claim 2 in which said photoconductive material contains a dye leachable therefrom by the oil phase in said oil-in-water emulsion.

8. In a photoconductographic process in which a positive image pattern of variations in electrical conductivities is produced in a layer comprising a photoconductive material, the steps of illuminating said layer with a desired image, electrophoretically depositing on said photoconductive material an imagewise reproduction of oil from a stabilized oil-in-water emulsion, giving said photoconductive material an overall exposure to light and electrophoretically depositing on said photoconductive material an ima'gewise layer of oil carrying a visible image-produc ing substance derived from a stabilized oil-in-water emul- 510B.

References Cited UNITED STATES PATENTS 11/1961 Johnson et al 20418 10/1963 Eastman et a1. 20418 JOHN H. MACK, Primary Examiner. T. TUFARIELLO, Assistant Examiner. 

